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91.
Summary The photodegradation behaviour of 12 nitrogen-containing herbicides (atrazine, cyanazine, terbuthylazine, terbutryn, EPTC,
buthylate, molinate, cycloate, vernolate, fenuron, chloroxuron, and methabenzthiazuron) has been examined. The compounds were
degraded completely when exposed to a mercury-vapour lamp; the degradation process was followed by consecutive GC measurements.
All the compounds studied had measurable photochemical activity, although actual and average degradation rates varied significantly.
All the compounds except terbutryn furnished more than one major degradation product, in different ratios.
Presented at Balaton Symposium '01 on High-Performance Separation Methods, Siófok, Hungary, September 2–4, 2001 相似文献
92.
Josef Ischtwan Peter Schwerdtfeger Sigrid D. Peyerimhoff Michael A. Collins Trygve Helgaker Poul Jørgensen Hans Jørgen Aa. Jensen 《Theoretical chemistry accounts》1994,89(2-3):157-168
Summary The intrinsic reaction-path, reactants, transition state and products for the reaction of NH (3–)+H2 (1
g
+
) NH2 (2B1)+H (2S) involving the lowest triplet electronic state of NH3 were calculated using multi-configuration (MC) SCF methods. The calculated change of internal energy for the reaction of 11.0 kcal mol–1 agrees with the experimental value within 2 kcal mol–1. The barrier to reaction is 23.4 kcal mol–1 high. The harmonic MCSCF reaction-path potential was calculated and canonical variational transition state theory calculations of the rate constants performed over a temperature range from 400 to 2500 K. The computed rate constants are generally two orders of magnitude smaller than those of the comparable reaction of OH with H2, whereas those of the reverse reaction are by a factor of 20 larger than those of OH2 with H. 相似文献
93.
《Journal of separation science》2003,26(11):1057-1062
The use of glass fiber as a support material for a surface compound serving to generate gaseous standard mixtures of ethene is described. The technique is based on the process of thermal decomposition of the surface compound in a desorber connected on‐line via a multi‐port valve to the calibrated device. The surface compound undergoes thermal decomposition at 245°C, yielding known amounts of ethene. The method enables on‐line preparation of a standard mixture immediately before the calibration step. Consequently, it can be also applied for the generation of standard mixtures containing volatile, malodorous, unstable, and toxic compounds. 相似文献
94.
A series of heat energy storage microcapsules was prepared using melamine-formaldehyde resin as the shell material and the mechanical properties of the shell were investigated. A phase change material whose melting point was 24 °C was used as core and the quantity of heat involved in phase transition was 225.5 J/g. Average diameter of the microcapsules varied from 5 to 10 μm, and the globular surface was smooth and compact. The mechanical properties of the shell were evaluated by observing the surface morphological structure change after application of pressure by means of scanning electron microscopy. When the mass ratio of the core and shell material is 3:1, a yield point of about 1.1×105 Pa was found and when the compression was increased beyond this point the microcapsules showed plastic behavior. This has been attributed to the cross-link density and to the high degree of reaction of the shell material. Different yield points subsequently reflected differences in the mechanical behavior. It was also found that the mechanical intensity of double-shell microcapsules was better than that of single shelled ones. 相似文献
95.
Development and validation of a stability-indicating HPLC method for the determination of degradation products in dipyridamole injection 总被引:1,自引:0,他引:1
Summary The development and subsequent validation of an isocratic high-performance liquid chromatographic (HPLC) procedure employing
ultraviolet (UV) detection for the determination of degradation products in Dipyridamole Injection is reported. The development
of this assay involved the evaluation of several factors including buffer type, ionic strength, pH, organic composition, and
column type. The described method is simple, reproducible, accurate, and selective. The precision, relative standard deviation
(RSD), amongst five sample preparations for total degradation products was not more than (NMT) 10.2 %, while the individual
degradation products were NMT 12.1%. Intermediate precision, as determined from fifteen sample preparations, generated by
two Analysts on different HPLC systems over three days, exhibited an RSD for total and individual degradation products of
8.2 % and NMT 27.5 %, respectively. The mean absolute recovery of dipyridamole using the described method is 102.1±1. 9%,
(mean±SD, n=12) over the concentration range of 0.03 % to 5.0 % of its label claim of 5 mg mL−1. The limit of detection and limit of quantitation were 0.1 and 0.3 μg mL−1, respectively. The linearity of the peak response was verified with respect to dipyridamole concentration over a range of
0.3 and 50 μg mL−1 (0.03 % to 5.0 % label claim). The Standard and Assay Preparations are stable for up to 48 hours at room temperature. The
selectivity was evaluated by subjecting the finished product (Dipyridamole Injection) to thermal, acidic, basic, oxidative
and fluorescent radiation stress conditions. No interference in the analysis of degradation products was observed, showing
the method is stability-indicating. 相似文献
96.
B. Pateyron M. F. Elchinger G. Delluc P. Fauchais 《Plasma Chemistry and Plasma Processing》1996,16(1):39-57
In most cases the energy dissipated in plasma jets used either,for heating or spraying is varied by changing the are current, the total gas floc+rate, and composition. However, when doing so, conditions are reached where the plasma jet may become supersonic. To predict such conditions or to characterize supersonic plasma jets the knowledge of the sound velocitya is mandatory The goal of this paper is to calculatea versus plasma forming gas composition, temperature, and pressure. Rigorous calculation would imply the knowledge of the chemical reaction kinetics, sound velocity depending strongly on this. Unfortunately such kinetics are generally lolknown for plasma jet floras and the only possibility is to determine the equilibrium sound velocitya calculated through the isentropic coefficient T. This coefficient has been calculated taking into account the dissociation and ionization reactions at equilibrium for temperatures ranging from 300 to 25,000 K and pressures between 0.1 and 1 Mpa for Ar, H2, He, Ar-He, Ar-H2, O2, N2, air, .steam, and methane.a often called the frozen sound velocity, was also calculated using (ratio of specific heats) instead of . 相似文献
97.
A high-performance thin-layer chromatographic (HPTLC) method is described for the determination of tributyltin compounds (bis(tri-n-butyltin) oxide, TBTO, and tri-n-butyltin naphthenate, TBTN) and their degradation products (dibutyltin and monobutyltin compounds). The organotin compounds are extracted from wood with ethanol containing 0.5% (v/v) of hydrochloric acid and the separation of the defferent kinds of organotin compounds is achieved by thin-layer chromatography. The sample spots are measured using a scanning densitometer after decomposing the organotin compounds to inorganic tin by ultraviolet irradiation and visualization of the spots with pyrocatechol violet. Applications of the method to detection and quantification of organotin compounds in preservative solutions, in recently impregnated wood, and in wood samples from five-year-old window frames are described. 相似文献
98.
用热分析技术TG-DTA(thermal gravimetric and differential thermal analysis)测定浆料中碳化硅粉体对分散剂聚乙二醇PEG(polyethylene glycol)的吸附量. 结果显示PEG在Ar气氛中411.5 ℃时完全分解; 碳化硅表面分散剂PEG的吸附量随着pH的增大而下降, 在较高pH下大多数分散剂仍存在于溶液中; 分散剂PEG的吸附量通过公式(1)进行计算. 该方法简单方便, 可以应用于测量氧化物或非氧化物吸附紫外-可见分光光度法不能测定的一些有机聚合物分子. 相似文献
99.
Plasma Thermal Conversion of Methane to Acetylene 总被引:2,自引:0,他引:2
Fincke J. R. Anderson R. P. Hyde T. Detering B. A. Wright R. Bewley R. L. Haggard D. C. Swank W. D. 《Plasma Chemistry and Plasma Processing》2002,22(1):107-138
This paper describes a re-examination of a known process for the direct plasma thermal conversion of methane to acetylene. Conversion efficiencies (% methane converted) approached 100% and acetylene yields in the 90–95% range with 2–4% solid carbon production were demonstrated. Specificity for acetylene was higher than in prior work. Improvements in conversion efficiency, yield, and specificity were due primarily to improved injector design and reactant mixing, and minimization of temperature gradients and cold boundary layers. At the 60-kilowatt scale cooling by wall heat transfer appears to be sufficient to quench the product stream and prevent further reaction of acetylene resulting in the formation of heavier hydrocarbon products or solid carbon. Significantly increasing the quenching rate by aerodynamic expansion of the products through a converging–diverging nozzle led to a reduction in the yield of ethylene but had little effect on the yield of other hydrocarbon products. While greater product selectivity for acetylene has been demonstrated, the specific energy consumption per unit mass of acetylene produced was not improved upon. A kinetic model that includes the reaction mechanisms resulting in the formation of acetylene and heavier hydrocarbons, through benzene, is described. 相似文献
100.